Preparation of amides

ABSTRACT

N-SUBSTITUTED AMIDES ARE PREPARED BY REACTING AN ESTER OF A CARBOXYLIC ACID WITH A PRIMARY OR SECONDARY AMINE IN THE PRESENCE OF A LEWIS ACID.

United States Patent Office 3,763,234 Patented Oct. 2, 1973 3,763,234 PREPARATION OF AMIDES William F. Brill, Skillman, N.J., assignor to Halcon International, Inc. No Drawing. Filed Dec. 3, 1970, Ser. No. 94,970 Int. Cl. C07e 103/30, 103/31, 103/76 US. Cl. 260-558 P 8 Claims ABSTRACT OF THE DISCLOSURE N-substituted amides are prepared by reacting an ester of a carboxylic acid with a primary or secondary amine in the presence of a Lewis acid.

This invention relates to the preparation of amides and is more particularly concerned with a process for producing amides by the aminolysis of esters.

Amides are a well-known class of compounds and they can be prepared by various methods such as the reaction of an acid chloride with ammonia or an amine, the partial hydrolysis of nitriles, aminolysis of esters, and the like. The synthetic route involving the aminolysis of an ester is useful for producing a variety of amides but this procedure generally gives low conversions to the desired product unless it is catalyzed. Various catalysts have been proposed, but they vary greatly in efiectiveness and some have the disadvantage of being relatively expensive.

It is an object of this invention to provide an improved method for the preparation of amides by the aminolysis of esters.

It has been discovered that the reaction between esters and amines to form amides is effectively catalyzed by Lewis acids and the process of this invention accordingly comprises the use of Lewis acids as catalysts in the preparation of amides by the reaction of an amine and an ester. The Lewis acids appear to have a unique activity in catalyzing this reaction.

The esters which may be employed in the process of this invention include the alkyl or aryl esters of aromatic carboxylic acids containing up to 12 carbon atoms, particularly the lower alkyl esters, i.e. those containing ester groups having up to 6 carbon atoms, and the alkyl and aryl esters of alkanoic acids, i.e. acids containing up to 6 carbon atoms, and especially the lower alkyl esters of lower alkanoic acids. The acids may be either monocarboxylic or polycarboxylic, e.g. dicarboxylic, acids. Esters of aromatic and alkanoic acids which may be employed in the process of this invention include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, methyl valerate, propyl caprylate, methyl pelargonate, phenyl acetate, methyl benzoate, propyl benzoate, phenyl benzoate, methyl laurate, butyl stearate, octyl butyrate, dimethyl adipate, dimethyl terephthalate, and the like.

Amines suitable for reaction with the ester in the process of this invention are primary and secondary amines, i.e. compounds having one or more primary or secondary amino groups, preferably primary amines, including monoamines, diamines, triamines, etc. Suitable amines include compounds of the general formula wherein R is an organic radical, e.g. an alkyl group, an aryl group, or an aralkyl group, the alkyl group containing up to 32 carbon atoms, preferably up to 12 carbon atoms, and the aryl or aralkyl groups, which include a benzene or a naphthalene neucleus substituted by alkyl radicals or aryl or aralkyl radicals, preferably containing up to carbon atoms. The alkyl group may be acyclic and of straight chain or branched structure, or it may be alicyclic. The R group may be interrupted by a hetero atom linkage, such as O or S, and may contain one or more primary or secondary amino groups. In the foregoing formula, R is preferably hydrogen but it may be an alkyl, aryl, or aralkyl group, as defined for R, and may be the same as R or it may be different from R in a given compound. When R and R are alkyl groups they may be joined together to form a heterocyclic link with the nitrogen atom to which they are attached. R and R' may also be substituted by non-interfering groups such as alkoxy, halo, and amido groups, and the like. One class of amines of the foregoing formula comprises diamines of the formula H NANH where A is an organic radical corresponding to R, e.g. an alkylene, arylene, or aralkylene radical, which may include hetero atom linkages. Examples of typical amines which may be used in the process of this invention include methyl amine, n-butyl amine, octyl amine, tetramethylene diamine, hexamethylene diamine, dibutyl amine, aniline, toluidine (0-, m-, or p-), 2,4 xylidine, 3,4 xylidine, 2,5-xylidine, 4 ethylaniline, 3 propylaniline, 1,3 diaminobenzene, 2,4-diaminotoluene, 4,4 diamino diphenyl methane, p-chloro aniline, 2,6 diamino toluene, 4,4 diaminodiphenyl, 2,4,4 triamino diphenyl ether, 2,6 diamino naphthalene, 1,5 diamino 2 methylpentane, benzyl amino, phenylethyl amine, piperidine, morpholine, piperazine, glycine, phenylalanine, phenoxyethyl amine, ethoxyethyl amine, 2 methoxy 5 chloro-aniline, 2- amino ethyl ether, 2-amino ethyl sulphide, cyclohexyl amine, and the like. Also included are amino-terminated polymers such as polyamines, e.g. polymeric compounds produced by condensation polymerization of aliphatic diamines, and the like, suitably containing up to amino groups or more. It will be understood from the foregoing that the amine which is reacted with the ester in accordance with the present invention may be of varied form and the amine needs only to be characterized as a primary or secondary amino compound, suitably having no interfering groups such as nitro groups. However, the preferred amino compounds are aromatic amines and the preferred esters are the lower alkyl esters.

As indicated above, the process of the present invention is characterized by the use of Lewis acids as catalysts. Lewis acids are well-known compounds and are defined, for example, in Physical Organic Chemistry by Jack Hine (1962McGraw-Hill Company, New York) and in Friedel-Crafts & Related Reactions by George A. Olah, volume I, (1963-Interscience Publishers, New York). Some examples of Lewis acids include antimony trichloride, aluminium chloride, antimony trifluoride, ferric chloride, antimony pentachloride, niobium pentachloride, tantalum tetrachloride, titanium tetrachloride, boron trifluoride, antimony pentafluoride, stannic fluoride, aluminum bromide, thallium trichloride, uranyl nitrate, uranium tetrachloride, uranium oxides, e.g. U0 and the like. Additional examples of Lewis acids are found in Friedel-Crafts & Related Reactions, referred to above, this publication being concerned primarily with Lewis acids of the salt type.

Preferred Lewis acids for use as catalysts in the process of this invention are those which are compounds of metals of Groups III-VIII of the Periodic Table, especially Groups V and VI, particularly the metals having atomic weights about 120. In general, the preferred Lewis acids are salts, e.g. halides, and the Lewis acids which have been found to be of particular utility and suitability are those which are compounds of uranium, including uranyl compounds, i.e. compounds containing the UO radical, especially the salts, e.g. uranium tetrachloride, uranyl chloride, uranyl nitrate, uranyl acetate, and the like.

When the amine and/or the ester is normally solid at room temperature, it is desirable that a solvent be employed. Suitable solvents are the usual inert organic compounds used as solvents in organic syntheses, such as aromatic hydrocarbons, e.g. benzene, toluene, xylene, and the like, aliphatic hydrocarbons such as hexane, octane, dodecane, and the like, halogenated aliphatic hydrocarrange, e.g. 0.1 to 48 hours, or longer, and the time of the reaction is not a critical aspect of the process.

Ordinarily, reaction times longer than 1 hour are more preferred but there is generally no advantage, from the standpoint of amide formation, in reaction times greater bons, such as 1,1,2 trichloroethane, 1,2,2 trifluoro- 5 than 24 hours. The reaction may be carried out batchethane, and the like, halogenated aromatic hydrocarbons, wise or it may be carried out continuously. Indeed, one such as monochlorobenzene, dichlorobenzene, trichloroof the features of the process is that it lends itself to conbenzene, and the like, ethers such as dibutyl ether, dioxane, tinuous operation by reason of the fact that all of the ethylene glycol disoamyl ether, diethyleneglycol diethyl 1O reactants in the appropriate proportions can be lntroether, and the like, and similar inert organic solvents. dlleed together into the y When at least one of the reactants is normally liquid at The reaction between the ester and the amine in acroom temperature, it is generally not nece sary t use cordance with the invention results in the concurrent rea solvent, since the liquid reactant can usually serve as lease of the alcohol pe g t0 the ester group h a solvent for the solid reactant, although an inert organic i ce the P e of Shell alcohol generally tends to solvent may employed if it is f u d that i f ilitat s hibit the reaction, it is preferred that the released alcohol the handling of the particular reaction medium. be removed from the y Thls can best be done y It is a feature f the invention, d one of i d providing the reaction vessel with a fractional distillation tages, that the reaction between the ester and the amine Column and y Carrying the ljeeetioh at the reflux proceeds smoothly at moderately elevated temperatures, temperature of the reactant mlxtlll'eh thle y h e.g. temperatures of 20 to 150 C., and there is no need eqhol y be removed Overhead contmueusly, 0r Interfor high temperatures to be used. Preferably a temperat' t t y, as desired- Altefnatlvely, the Teaetloh y he tu e within th range of 80 to 110 C. is employed. It Initially carried out below the reflux temperature and will be understood, however, that more elevated temperathen heated to the reflIlX temperature When it is fleshed tures can be employed if desired, e.g. temperatures up to to remove e alcohol and to accelerate the Teeetleh- 250 C. and above, but temperatures should be below tollowlhg speeifie eXamPIeS of Practical application those at which decomposition of a reactant or a reaction W e Q Provide a fuller eppl'eeletioh 0f the invenproduct occurs. Pressure is not a parameter of the procbut 1t 18 to understood that these eXemPIeS are ess and the operation may ordinarily be carried out at given y ar Of 111ustrat10a ye are not to be natmospheric pressure. However, super atmospheric pres- Strtled as llmltatlve 0f the lnventlon. sures may be employed if desired in cases in which one or more of the reactants is relatively low boiling but, or- EXAMPLE I dinarily, pressures greater than two atmospheres are not I a 50 1 fla k fitted to a vi l are necessary. charged 13.6 g. methyl benzoate, 9.3 g. aniline and 0.5 Although the reaction can be carried out with stoichiouranyl chloride The Solution is r fl x d (pot tempera. metric quantities of the reactants, one of the reactants ture 135 C h h h column d h l i m y be in excess- Whil the amount Of excess reactant moved overhead. After two hours the reaction is stopped, may vary, it is preferred that the excess be limited to a and the reaction solution cooled. There is obtained 3.5 g. maximum of 50 mols, preferably 15 mols, of the reactant f N-phenyl benzamide, in excess per mol of the other reactant.

The amount of Lewis acid catalyst employed can vary, EXAMPLE II and eveli very Small i q are effective to catalyze Following the procedure and using the apparatus dethe reaction. However, it 1s generally des rable to use at scribed in Example I the flask is charged with 4 least f mol f m of Lewls acld based i t dimethyl terephthalate, 6 g. ethylene diamine and 0.5 g. quanflty of f t h Preent at most m uranyl nitrate. The solution is refluxed (pot temperature meme quaFtlty {g is 9 m F i g 100 C.) and methanol is removed overhead. After 1 zmounts Lew1s 2 genera Y hour the reaction is stopped and the solid diamide (20 econorfnc consl eratlon? as a genera e ere g.) is washed with chloroform and recovered. is no particular advantage 1n using amounts greater than 25 mol percent. The optimum amount of catalyst will EXAMPLE n vary with reaction conditions and with the particular Lewis acid used but ordinarily it is advantageous to use Following the procedure of Example I, except that the from 0.1 to 10 mol percent of the Lewis acid, preferably reaction is carried out at 80 C. without alcohol removal, 0.5 to 10%. various esters and amines are reacted with Lewis acid The reaction between the amine and the ester in the catalysts. The data for these experiments are shown in presence of Lewis acid, 1n accordance with the invention, Table I below. In the table, results of control experiments may be earned out in any convenient reaction vessel and, carried out under the same conditions, but without the 1f super atmospheric pressures are to be employed, the Lewis acid catalysts, are also shown. The letter N indivessel is suitably constructed to withstand the maximum cates that no detectable product was formed in the conpressure to be employed. The reaction is ordinarily control experiment while the letter L indicates that some ducted by introducing the two reactants and the catalyst product was formed but in characteristically lesser quaninto the reaction vessel and then heating the reactant tity. In ea h case, except Where otherwise indicated, the mixture at the desired reaction temperature for a suitable ester and the amine are used in 1:1 mol ratio, and 0.05 period of time. The reaction time may vary over a wide mol of catalyst per mol of ester is employed.

TABLE I Time, Con- Ester Amine Catalyst hrs. Product trol Methyl butyrate Aniline U020]; 17 N-phenyl butyramide.-. N Butyl acetate.-. ..d0 U014 35 Acetanilide N Phenylacetat U014 17 -do N Methyl acetat UOz(NO )r--4H;O 31 do- L D sboh 119 -do L 35 ..do L 17 N-butyl butyrarm L 4 N-butyl acetamide L 1 M01 ratio ester/amine=5:2.

What is claimed is:

1. A process for producing an amide which comprises reacting a carboxylic acid ester with a primary or secondary amine in the presence of a Lewis acid catalyst, said ester being an alkyl or aryl ester of a monocarboxylic or poly-carboxylic aromatic or alkanoic acid containing up to 12 carbon atoms, said amine being an alkyl, aryl or aralkyl primary or secondary amine containing up to 32 carbon atoms in the case of an alkyl amine and containing up to 15 carbon atoms in the case of an aryl or aralkyl amine, and said Lewis acid being a halide of antimony, aluminum, iron, niobium, tantalum, titanium, boron, tin or thallium, a uranium tetrahalide, uranyl halide, uranyl nitrate, uranyl acetate, or uranium dioxide.

2. A process as defined in claim 1, wherein said ester is an alkyl ester.

3. A process as defined in claim 1, wherein said amine is an aryl amine.

4. A process as defined in claim 1, wherein said catalyst is a uranium tetrahalide, uranyl halide, uranyl nitrate, uranyl acetate, or uranium dioxide.

5. A process as defined in claim 1, wherein said ester is an alkyl ester, said amine is an aryl amide and said catalyst is a uranium tetrahalide, uranyl halide, uranyl nitrate, uranyl acetate, or uranium dioxide.

6. A process as defined in claim 1, wherein said ester is used in an amount which is in excess in relation to the stoichiometric quantity with respect to the amine.

7. A process as defined in claim 1, wherein the reaction is carried out at substantially atmospheric pressure at a temperature of up to about C.

8. A process as defined in claim 1, wherein the alcohol liberated is removed during the course of the reaction.

HARRY I. MOATZ, Primary Examiner US. Cl. X.R.

260-247], 268 C, 293.8, 518 R, 534 R, 558 R, 558 A, 561 R, 561A, 562 R, 562 P, 562 A 

